158 DIFFICULTIES OF THE TIiEOBT. 



CHAPTEE VI. 



DIFFICULTIES OF THE THEORY. 



Difficulties of the theory of descent with modification — Absence or 

 rarity of transitional varieties — Transitions in habits of life — 

 Diversified habits in the same species — Species with habits 

 widely different from those of their allies — Organs of extreme 

 perfection — Modes of transition — Cases of difficulty — Natura non 

 facit saltum — Organs of small importance — Organs not in all 

 cases absolutely perfect — The law of Unity of Type and of the 

 Conditions of Existence embraced by the theory of Natural 

 Selection. 



Long before the reader has arrived at this part of my 

 work, a crowd of difficulties will have occurred to him. 

 Some of them are so serious that to this day I can hardly 

 reflect on them without being in some degree staggered; 

 but, to the best of my judgment, the greater number are 

 only apparent, and those that are real are not, I think, 

 fatal to the theory. 



These difficulties and ejections may be classed under the 

 following heads: First, why, if species have descended from 

 other species by fine gradations, do we not everywhere see 

 innumerable transitional forms? Why is not all nature in 

 confusion, instead of the species being, as we see them, 

 well defined? 



Secondly, is it possible that an animal having, for 

 instance, the structure and habits of a bat, could have been 

 formed by the modification of some other animal with 

 widely different habits and structure? Can we believe that 

 natural selection could produce, on the one hand, an organ 

 of trifling importance, such as the tail of a giraffe, which 

 serves as a fly-flapper, and, on the other hand, an organ so 

 wonderful as the eye? 



Thirdly, can instincts be acquired and modified through 

 natural selection? AVhat shall we say to the instinct which 



